fix: preserve panic behavior in needless_range_loop lint; update .stderr tests

Author: Aadi11z

clippy_lints/src/loops/needless_range_loop.rs

@@ -166,6 +166,12 @@ pub(super) fn check<'tcx>(
             } else {
                 let repl = if starts_at_zero && take_is_empty {
                     format!("&{ref_mut}{indexed}")
+                } else if !take_is_empty {
+                    // Adding condition for when 'take' is not empty Fixing `.take(n)` with slicing to preserve panic semantics
+                    format!(
+                        "{indexed}[..{}].{method}(){method_2}",
+                        snippet(cx, end.unwrap().span, "..")
+                    )
                 } else {
                     format!("{indexed}.{method}(){method_1}{method_2}")
                 };
@@ -181,6 +187,10 @@ pub(super) fn check<'tcx>(
                             vec![(pat.span, "<item>".to_string()), (span, repl)],
                             Applicability::HasPlaceholders,
                         );
+                        diag.note(
+                            "this suggestion preserves panic behavior, but the panic will occur \
+                            before iteration if the upper bound exceeds the collection length",
+                        );
                     },
                 );
             }

tests/ui/needless_range_loop.stderr

@@ -4,6 +4,7 @@ error: the loop variable `i` is only used to index `vec`
 LL |     for i in 0..vec.len() {
    |              ^^^^^^^^^^^^
    |
+   = note: this suggestion preserves panic behavior, but the panic will occur before iteration if the upper bound exceeds the collection length
    = note: `-D clippy::needless-range-loop` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::needless_range_loop)]`
 help: consider using an iterator
@@ -18,6 +19,7 @@ error: the loop variable `i` is only used to index `vec`
 LL |     for i in 0..vec.len() {
    |              ^^^^^^^^^^^^
    |
+   = note: this suggestion preserves panic behavior, but the panic will occur before iteration if the upper bound exceeds the collection length
 help: consider using an iterator
    |
 LL -     for i in 0..vec.len() {
@@ -30,6 +32,7 @@ error: the loop variable `j` is only used to index `STATIC`
 LL |     for j in 0..4 {
    |              ^^^^
    |
+   = note: this suggestion preserves panic behavior, but the panic will occur before iteration if the upper bound exceeds the collection length
 help: consider using an iterator
    |
 LL -     for j in 0..4 {
@@ -42,6 +45,7 @@ error: the loop variable `j` is only used to index `CONST`
 LL |     for j in 0..4 {
    |              ^^^^
    |
+   = note: this suggestion preserves panic behavior, but the panic will occur before iteration if the upper bound exceeds the collection length
 help: consider using an iterator
    |
 LL -     for j in 0..4 {
@@ -66,10 +70,11 @@ error: the loop variable `i` is only used to index `vec2`
 LL |     for i in 0..vec.len() {
    |              ^^^^^^^^^^^^
    |
+   = note: this suggestion preserves panic behavior, but the panic will occur before iteration if the upper bound exceeds the collection length
 help: consider using an iterator
    |
 LL -     for i in 0..vec.len() {
-LL +     for <item> in vec2.iter().take(vec.len()) {
+LL +     for <item> in vec2[..vec.len()].iter() {
    |
 
 error: the loop variable `i` is only used to index `vec`
@@ -78,6 +83,7 @@ error: the loop variable `i` is only used to index `vec`
 LL |     for i in 5..vec.len() {
    |              ^^^^^^^^^^^^
    |
+   = note: this suggestion preserves panic behavior, but the panic will occur before iteration if the upper bound exceeds the collection length
 help: consider using an iterator
    |
 LL -     for i in 5..vec.len() {
@@ -90,10 +96,11 @@ error: the loop variable `i` is only used to index `vec`
 LL |     for i in 0..MAX_LEN {
    |              ^^^^^^^^^^
    |
+   = note: this suggestion preserves panic behavior, but the panic will occur before iteration if the upper bound exceeds the collection length
 help: consider using an iterator
    |
 LL -     for i in 0..MAX_LEN {
-LL +     for <item> in vec.iter().take(MAX_LEN) {
+LL +     for <item> in vec[..MAX_LEN].iter() {
    |
 
 error: the loop variable `i` is only used to index `vec`
@@ -102,10 +109,11 @@ error: the loop variable `i` is only used to index `vec`
 LL |     for i in 0..=MAX_LEN {
    |              ^^^^^^^^^^^
    |
+   = note: this suggestion preserves panic behavior, but the panic will occur before iteration if the upper bound exceeds the collection length
 help: consider using an iterator
    |
 LL -     for i in 0..=MAX_LEN {
-LL +     for <item> in vec.iter().take(MAX_LEN + 1) {
+LL +     for <item> in vec[..MAX_LEN].iter() {
    |
 
 error: the loop variable `i` is only used to index `vec`
@@ -114,10 +122,11 @@ error: the loop variable `i` is only used to index `vec`
 LL |     for i in 5..10 {
    |              ^^^^^
    |
+   = note: this suggestion preserves panic behavior, but the panic will occur before iteration if the upper bound exceeds the collection length
 help: consider using an iterator
    |
 LL -     for i in 5..10 {
-LL +     for <item> in vec.iter().take(10).skip(5) {
+LL +     for <item> in vec[..10].iter().skip(5) {
    |
 
 error: the loop variable `i` is only used to index `vec`
@@ -126,10 +135,11 @@ error: the loop variable `i` is only used to index `vec`
 LL |     for i in 5..=10 {
    |              ^^^^^^
    |
+   = note: this suggestion preserves panic behavior, but the panic will occur before iteration if the upper bound exceeds the collection length
 help: consider using an iterator
    |
 LL -     for i in 5..=10 {
-LL +     for <item> in vec.iter().take(10 + 1).skip(5) {
+LL +     for <item> in vec[..10].iter().skip(5) {
    |
 
 error: the loop variable `i` is used to index `vec`
@@ -186,10 +196,11 @@ error: the loop variable `i` is only used to index `a`
 LL |     for i in 0..MAX_LEN {
    |              ^^^^^^^^^^
    |
+   = note: this suggestion preserves panic behavior, but the panic will occur before iteration if the upper bound exceeds the collection length
 help: consider using an iterator
    |
 LL -     for i in 0..MAX_LEN {
-LL +     for <item> in a.iter().take(MAX_LEN) {
+LL +     for <item> in a[..MAX_LEN].iter() {
    |
 
 error: aborting due to 16 previous errors

tests/ui/needless_range_loop2.stderr

@@ -4,12 +4,13 @@ error: the loop variable `i` is only used to index `ns`
 LL |     for i in 3..10 {
    |              ^^^^^
    |
+   = note: this suggestion preserves panic behavior, but the panic will occur before iteration if the upper bound exceeds the collection length
    = note: `-D clippy::needless-range-loop` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::needless_range_loop)]`
 help: consider using an iterator
    |
 LL -     for i in 3..10 {
-LL +     for <item> in ns.iter().take(10).skip(3) {
+LL +     for <item> in ns[..10].iter().skip(3) {
    |
 
 error: the loop variable `i` is only used to index `ms`
@@ -18,6 +19,7 @@ error: the loop variable `i` is only used to index `ms`
 LL |     for i in 0..ms.len() {
    |              ^^^^^^^^^^^
    |
+   = note: this suggestion preserves panic behavior, but the panic will occur before iteration if the upper bound exceeds the collection length
 help: consider using an iterator
    |
 LL -     for i in 0..ms.len() {
@@ -30,6 +32,7 @@ error: the loop variable `i` is only used to index `ms`
 LL |     for i in 0..ms.len() {
    |              ^^^^^^^^^^^
    |
+   = note: this suggestion preserves panic behavior, but the panic will occur before iteration if the upper bound exceeds the collection length
 help: consider using an iterator
    |
 LL -     for i in 0..ms.len() {
@@ -42,10 +45,11 @@ error: the loop variable `i` is only used to index `vec`
 LL |     for i in x..x + 4 {
    |              ^^^^^^^^
    |
+   = note: this suggestion preserves panic behavior, but the panic will occur before iteration if the upper bound exceeds the collection length
 help: consider using an iterator
    |
 LL -     for i in x..x + 4 {
-LL +     for <item> in vec.iter_mut().skip(x).take(4) {
+LL +     for <item> in vec[..x + 4].iter_mut().take(4) {
    |
 
 error: the loop variable `i` is only used to index `vec`
@@ -54,10 +58,11 @@ error: the loop variable `i` is only used to index `vec`
 LL |     for i in x..=x + 4 {
    |              ^^^^^^^^^
    |
+   = note: this suggestion preserves panic behavior, but the panic will occur before iteration if the upper bound exceeds the collection length
 help: consider using an iterator
    |
 LL -     for i in x..=x + 4 {
-LL +     for <item> in vec.iter_mut().skip(x).take(4 + 1) {
+LL +     for <item> in vec[..x + 4].iter_mut().take(4 + 1) {
    |
 
 error: the loop variable `i` is only used to index `arr`
@@ -66,6 +71,7 @@ error: the loop variable `i` is only used to index `arr`
 LL |     for i in 0..3 {
    |              ^^^^
    |
+   = note: this suggestion preserves panic behavior, but the panic will occur before iteration if the upper bound exceeds the collection length
 help: consider using an iterator
    |
 LL -     for i in 0..3 {
@@ -78,10 +84,11 @@ error: the loop variable `i` is only used to index `arr`
 LL |     for i in 0..2 {
    |              ^^^^
    |
+   = note: this suggestion preserves panic behavior, but the panic will occur before iteration if the upper bound exceeds the collection length
 help: consider using an iterator
    |
 LL -     for i in 0..2 {
-LL +     for <item> in arr.iter().take(2) {
+LL +     for <item> in arr[..2].iter() {
    |
 
 error: the loop variable `i` is only used to index `arr`
@@ -90,6 +97,7 @@ error: the loop variable `i` is only used to index `arr`
 LL |     for i in 1..3 {
    |              ^^^^
    |
+   = note: this suggestion preserves panic behavior, but the panic will occur before iteration if the upper bound exceeds the collection length
 help: consider using an iterator
    |
 LL -     for i in 1..3 {